Various coils and capacitors are used widely as components in electro-technical devices, such as oscillators and filters. With increasing frequencies the losses of capacitors and coils, however, increase to such an extent that various cavity and coaxial resonators and dielectric resonators are the only alternative in terms of losses.
Particularly within the frequency range from 1 to 10 GHz, where the resonator according to the invention is to be used, cavity resonators are often large and require special components with expensive packings. The use of dielectric resonators in turn results in a structure having the disadvantages of e.g. being difficult to assemble and difficult to tune electrically. Having low losses, coaxial resonators are the most widely used especially at high powers. The losses of coaxial resonators decrease with increasing resonator sizes while their power handling capacity increases. A disadvantage of a resonator made of a conventional coaxial conductor is its difficult frequency adjustment, but if the resonator is provided with an inner conductor open in the middle, the frequency is easy to adjust by an adjusting screw or a similar adjusting means, which extends inside the inner conductor of the resonator. The present invention, in fact, is based on a coaxial resonator having the advantages described above and allowing the frequency to be adjusted as described above.
In the prior art resonator structure having the above-described properties, the inner conductor is implemented as a thick-wall metal tube into which the frequency adjusting means penetrates. Devices based on this basic structure (e.g. oscillators) have previously been implemented by bringing the active components surrounding the resonator, such as transistors, varactors and Gunn diodes, into galvanic contact with the side of the inner conductor. This has required the use of expensive (special) components. If the resonator has been used in a filter, it has been necessary to connect the inner conductor to an output connector by a separate conductor wire. Coupling to the inner conductor of the resonator has thus involved a complicated structure difficult to implement and possibly also requiring components more expensive than usually.